Serotonin syndrome represents a recently described complication of drug therapy with medication(s) that increase serotonin neurotransmission. This syndrome consists of alterations in cognition, automatic nervous system function, and neuromuscular function. It is rarely fatal and usually responds to supportive care alone. This article presents two illustrative cases of serotonin syndrome and reviews the known medical literature on this topic. In addition, it also discusses serotonin pharmacology, physiology, and its receptor classification.